When making the film version of 2001: A Space Odyssey, Stanley Kubrick and Arthur C. Clarke consulted with IBM. Given that one of the film's major plot points centers on an insane artificial intelligence, Kubrick was a tad bit worried that IBM might be displeased with their association with the film.

In August 1966, Kubrick wrote to Roger Caras, who was, at the time, vice president of Kubrick's production company, asking if IBM was clear on HAL's murderous sentiments. You can read Caras' full reply over at Letters of Note, but the gist was that IBM was fine as long as it was credited as just one among many consultants and that IBM was not "associated with equipment failure."

Of course, there are other reasons that people would associate HAL with IBM after the film's release, including that each of the letters in "HAL" are one letter off from "IBM." Clarke has denied that this was intentional, saying in his book The Lost Worlds of 2001:

As is clearly stated in the novel (Chapter 16), HAL stands for Heuristically programmed ALgorithmic computer. However, about once a week some character spots the fact that HAL is one letter ahead of IBM, and promptly assumes that Stanley and I were taking a crack at the estimable institution ... As it happened, IBM had given us a good deal of help, so we were quite embarrassed by this, and would have changed the name had we spotted the coincidence.

That still leaves the business of HAL singing "Daisy Bell" (the favorite tune of IBM 704) as his death song, but perhaps that is a matter for another correspondence exchange.